Superparamagnetic γ-Fe2O3-SiO2 Nanocomposites from Fe2O3-SiO2-PVA Hybrid Xerogels: Characterization and MRI Preliminary Testing

Background: In order to be suitable for biomedical applications, the iron oxide based magnetic materials require appropriate characteristics such as superparamagnetic behaviour, high saturation magnetization, high specific surface area, small particle size and narrow distribution. Objective: The objective of the present study was to find the optimum conditions for obtaining iron oxide-silica nanocomposites with superparamagnetic behaviour by thermolysis of sol-gel derived inorganic-organic hybrid xerogels. Method: The tetraethylorthosilicate, TEOS, and iron (III) acetylacetonate precursors were processed at room temperature by acid catalysed sol-gel route in the presence of polyvinyl alcohol (molecular weight of 145000) as an additive. The thermal treatment at 180 degrees C, 220 degrees C, 260 degrees C, 300 degrees C, 400 degrees C and 500 degrees C respectively, of obtained inorganic-organic hybrid xerogel resulted in six Fe2O3-SiO2 (20% Fe2O3-target composition) nano-composite samples. All the samples were investigated by means of X-ray diffraction technique, transmission electron microscopy, Mossbauer spectroscopy, and submitted to magnetic measurements. Results: The maghemite unique crystalline phase was obtained at 300 degrees C along with a certain amount of amorphous iron oxide. By further raising the calcination temperature, this initialized the gamma-to-Fe2O3 transition process. At 400 degrees C, the maghemite and hematite coexist, and at 500 degrees C only the hematite crystalline phase was found. Conclusion: Both structural and magnetic properties of the nanocomposite sample annealed at 260 degrees C, recommend it. The sample consists in gamma-Fe2O3 phase exhibiting superparamagnetic behavior with approx. 48 emu/g saturation magnetization value and approx. 10 nm average particle diameter. A promising response was obtained when the sample was tested as a contrast agent in medical imaging application.